1. Field of the Invention
The present invention relates to a plug used in connectors for making electrical connections, e.g. for connecting electrical cables. The plug or the connector including such a plug according to the invention may be used with solar cell modules.
2. Description of Background Information
Electrical power generating systems employing solar energy have drawn much attention in recent years. Such systems use solar cells to produce electrical power for domestic appliances. The solar cells are arranged in panels installed, e.g. on a building roof, and produce direct current, which is subsequently transformed into alternating current through an inverter, a power transformer, an accumulator, etc. The alternating current thus produced is used to feed electrical appliances.
A solar cell panel includes a plurality of solar cell modules connected in series. The modules are connected by purpose-designed connectors each consisting of a plug and socket. Usually, a plurality of solar cell panels are connected together to form a solar cell array. The solar cell panels can also be connected together using connectors similar to those used for connecting solar cell modules.
With this kind of connector, there is a risk that personnel can receive electrical shocks by touching the terminal portion of the plug. In the construction of the aforementioned solar energy based electrical power generating systems, solar cell modules are first installed e.g. on a roof, and only afterwards the electrical connections are made. When the solar cell modules are mounted, lead lines between the modules may already be at a certain voltage level. If personnel touch these lead lines, they risk receiving an electrical shock.
Various measures have been taken in order to avoid risks of electrical shock. For example, according to a prior art device disclosed in Japanese Patent Application published under number HEI-8-203593, the plug and the socket that form a connector are respectively coated with an insulator. For instance, the conductive core of the plug is covered with a cylindrical insulator (housing). In addition, the end opening of the housing is capped with a lid, so that the edge of the plug element is not exposed. As a result, personnel can safely touch the connectors with their bare hands when installing them.
However, the structure of the insulator becomes rather complicated with this plug configuration. Moreover, supplementary work is needed for opening or closing the lid.
Another prior art device is disclosed in Japanese Patent Application published under number HEI-9-148004. According to this disclosure, a cable is first led out from a solar cell module, and the end portion of this cable is connected to a plug core. The end portion of the plug core is then fitted with a cylindrical insulator having a diameter about the same as, or slightly smaller than, the outer diameter of the plug core. By adopting such protective means, a metallic portion is prevented from being exposed at the end opening of the cylindrical insulator.
As the electrically conductive plug tip is not exposed, there is no risk of electrical shock, e.g. by finger contact. However, the insulator disclosed in Japanese Application HEI-9-148004 is fitted onto the plug tip by threading or other equivalent means. Therefore, the plug core or the insulator must be configured specifically for that kind of fastening. Moreover, fitting the insulator may require additional labor. Instead of being threaded, the plug tip may be cut into a sharpened form and covered with an insulating resin. However, the cutting work in this case is time consuming and thus leads to increased production costs.